Vector drive for vapor compression systems

ABSTRACT

Described is a vector control system for a vapor compression circuit. The vector control system may monitor the vapor compression circuit and adjust the speed of one or more motors to increase efficiency by taking into account the torque forces placed on a compressor motor.

INCORPORATION BY REFERENCE TO ANY RELATED APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

This application is a continuation of U.S. patent application Ser. No.15/204,879, entitled VECTOR DRIVE FOR VAPOR COMPRESSION SYSTEMS, nowissued as U.S. Pat. No. 10,627,145 on Apr. 21, 2020, the disclosure ofwhich is hereby incorporated by reference herein in its entirety for allpurposes and forms a part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

Aspects of the invention relate to systems and methods for controlling avapor compression system. More particularly, aspects of the inventionrelate to vapor compression systems that can be controlled to increasetheir efficiency by modulating the speed and torque placed on acompressor.

Description of the Related Art

Vapor compression systems include Heating, Ventilation and AirConditioning (HVAC) systems, refrigeration systems and heat pump systemsare widely used in many industrial and residential applications. Morerecent systems can use variable speed compressors, variable positionvalves, and variable speed fans to increase the flexibility ofcontrolling the vapor compression cycle.

An operation cycle of the vapor compression system starts by using acompressor to compress the gaseous refrigerant to a high-temperature,high-pressure vapor state. The refrigerant then flows into a condenser.Because the air flowing over the condenser coils is cooler than therefrigerant, the refrigerant cools to form a high-pressure, somewhatreduced temperature liquid when exiting the condenser. This is typicallycalled the “high side” of the vapor compression cycle.

The liquid refrigerant then passes through an expansion valve thatdecreases the pressure. The expansion valve may be a pulsing expansionvalve that can accurately control the refrigerant without overshootingand hunting during dynamic operating conditions. One type of pulsingexpansion valve can be found in U.S. Pat. No. 6,843,064, issued Jan. 18,2005 which is hereby incorporated by reference in its entirety. Thelow-pressure refrigerant boils at a lower temperature, so the airpassing over the evaporator coils heats the refrigerant. Thus, the airis cooled down, and the low-pressure liquid refrigerant is converted toa low-pressure vapor. This low-pressure, low-temperature vapor thenenters the compressor, and the operation of the vapor compression systemcontinues to cycle. This is typically called the “low side” of the vaporcompression cycle.

Vapor compression systems take advantage of the latent heat ofvaporization of liquids that have a boiling point lower than the desiredtemperature to be managed. The four major elements of the system are thecompressor, condenser, expansion valve, and evaporator. In theevaporator, the refrigerant vaporizes at a low temperature, absorbingheat from the environment. At the evaporator, the refrigerant is a lowtemperature vapor. The vapor then passes through the compressor, whereit is brought to high pressure and a temperature typically 10° C. to 15°C. higher than ambient. This hot vapor is converted to liquid in thecondenser where heat is rejected to ambient air. The hot liquidrefrigerant then exits the condenser and passes through an expansionvalve, dropping the refrigerant to a low pressure and temperature. Thelow-temperature, low-pressure liquid refrigerant then enters theevaporator and the cycle begins again.

Current systems can use variable refrigerant flow (VRF) technology inwhich the speed of a compressor is varied to depending on theload-induced capacity requirements on the system. Such VRF operation hasthe advantage of reducing, or avoiding, repetitive on/off cycling of thecompressor in prior systems that did not use VRF technology. Therepetitive cycling of the compressor can result in energy inefficiencysince the compressor may need to start-up and shut down repeatedly sothat the refrigerant pressure within the device can remain atequilibrium and the system can re-establish the partial, or total, lossof temperature difference between an evaporator and a condenser withinthe system.

SUMMARY OF THE INVENTION

One embodiment is a vapor compression system that includes: at least onecompressor having an inlet pressure and an outlet pressure; at least oneevaporator; at least one condenser; a refrigerant expansion device; anda vector control system configured to control the speed of thecompressor to satisfy a load and also configured to control the torqueof the compressor by adjusting the airflow across the evaporator, thecondenser, or both.

Another embodiment is a vector control system for increasing theefficiency of a vapor compression system. This embodiment includes: aprocessor and a control module having instructions configured to be runon the processor, wherein the instructions adjust refrigerant flow and acompression ratio in the vapor compression system based on controllingthe speed of one or more motors to influence torque of each of thesubject motors by referencing the speed, torque and energy efficiencycharacteristics of the subject motors as input parameters to control foroptimal energy efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of a HVAC system thathas a vector control system.

FIG. 2 is a schematic diagram of a vector control system according toone embodiment of the invention.

FIG. 3 is a line graph showing that vector drive technology as discussedherein resulted in higher efficiency at partial speeds and loads.

DETAILED DESCRIPTION

Embodiments of the invention relate to vapor compression systems, suchas air conditioners, heat pumps and refrigeration systems that employ avector control system for increased efficiency. Embodiments are notlimited to single stage vapor compression systems, but also includemulti-stage systems which employ two or more compressors between the lowsaid and high side refrigerant heat exchangers. These systems can bereferred to as cascaded systems, and are further described in U.S. Pat.No. 9,239,174, which is hereby incorporated by reference in itsentirety. The invention further applies to vapor compression cycles withintermediate pressure vapor or liquid injection into the compressor aswell as educator enhanced cycles. The vapor compression system may alsoinclude one or more reversing valves to operate as a cooling and heatingpump. A reversing valve is a type of valve that may be a component in aheat pump. The one or more reversing valves allow the system to changethe direction of refrigerant flow within the system. By reversing theflow of refrigerant, the heat pump refrigeration cycle is changed fromcooling to heating. This allows a home or building to be heated andcooled by a single piece vapor compression system, using the samehardware.

Embodiments of the Vector Control System (VCS) described herein expandthe one-dimensional speed control of a vapor compression system into atwo dimensional speed and torque control system. Incorporating torquecontrol into the system allows for optimal use of the compressor motorto increase the overall system efficiency. The VCS may control motorswithin the system such as the compressor motor as well as fan and blowermotors within a vapor compression system. The VCS optimization processcan take into account characteristics of the compressor motor'sperformance as a function of speed, compression ratio and absolutepressures. The VCS may also take into account other system motors in thesystem to improve the efficiency of condenser fan(s) and in some casesevaporator fans or blowers. Vector Drive control constitutes a twodimensional energy efficiency optimization incorporating refrigerantflow as well as high side (condenser) air flow and, in some instanceslow side (evaporator) air flow, deriving the best system energyefficiency obtainable at any given load and temperature condition.

In one example, an air conditioner operating condition thatconventionally calls for a certain predetermined compressor speed at aset condition is improved by operating the compressor at a lower torquesetting while using the same refrigerant flow. Although the system wouldbe using less torque the resultant cooling capacity would remain thesame because the refrigerant flow through the vapor compression circuitdoesn't change. The lower compressor torque could be achieved byincreasing the airflow of a condenser fan. This increased airflow wouldlower the condenser temperature and pressure which may decrease thetorque required by the compressor to compress the refrigerant. Dependingon the compressor motor and condenser fan characteristics, theadditional energy required to increase the fan speed could be less thanthe energy saved by reducing the torque on the compressor. Thus, in thisembodiment, the VCS would evaluate the energy required to increase thecondenser fan speed and balance that against the energy saved bylowering the torque on the compressor. If the energy saved by reducingthe torque on the compressor was greater than the energy required toincrease the fan speed, then the VCS would increase the condenser fan tosave energy overall.

In other embodiments, reducing the compressor torque may reduce theoverall efficiency if the energy required to increase the speed of thecondenser fan is more than the energy required to operate the compressorat a higher torque. Thus, the VCS system can vary different componentsin different systems within the vapor compression circuit to increasethe overall system efficiency by modulating the torque placed ondifferent motors and by adjusting the speed of the various motors togive the optimum energy efficiency.

In order to achieve such performance advantages, the performancecharacteristics as a function of speed and torque for all the subjectmotor systems is first determined. Commonly these motors include thecompressor, condenser fan(s) or condenser blower(s) and at timesevaporator fan(s) or evaporator blower(s).

TABLE 1 Exemplary Motor Characteristics Compressor Blower CondenserMotor Motor Motor Voltage (VAC) 230 230 230 Torque (lb · in) 175 17.526.2 Speed (RPM) 1800 3600 3600 Power (HP) 5 1 1.5

Once the characteristics of these motors are established they can beentered into the appropriate equations, approximations or tables, asindicated below. These VCS system then uses these equations,approximations and tables as input parameters to determine how tocontrol the various vapor compression system motors under a givenrunning condition. A properly optimized system would includeconsideration of all motor/compressor, motor/fan, ambient temperature,humidity, and load conditions to determine the best operating mode torun the system with the highest efficiency. Such a process may alsoinclude consideration of the operating frequencies for compressormotor(s) and fan motors to achieve higher capacities, often referred toas peak capacities, by overclocking motor operating frequencies.However, it should be realized that such overclocking does not alwaysachieve a higher overall energy efficiency but instead is implemented toachieve a temporary peak capacity to overcome adverse operatingconditions.

An additional embodiment that can lead to dramatic energy savings is theestablishment of variable sensible heat ratios. Accounting for thelatent and sensible heat ratio is important for equipment that is usedin different climates, e.g. hot dry climates and humid climates. Therelative humidity can be determined with known sensors based on dry bulband wet bulb temperatures and become an input into the operatingparameter data of the VCS. Alternately, if no such sensors areavailable, the system can be set to different humidity conditions by asoftware or hardware switch or pre-set for various degrees of humidityas expected to be typically encountered in the target operatingenvironment. In one embodiment, the system carefully monitors theevaporator temperature and airflow over the system. For example, theairflow can be increased at a somewhat higher evaporator temperature toremove a larger than average amount of humidity from the air. This inturn will increase the low side pressure and thus reduce the compressionratio for the compressor.

Additionally, the VCS can include further energy efficiency realizationduring transients when the speed of the motors is changed. This canoccur when the operating frequency is less than a nominal frequency.Transients can be induced by changing temperature, changing loads, andstarts and stops. When the VCS is used to start or change the speed ofone or more motors, a low frequency, low voltage power signal isinitially applied to each motors. In some embodiments, the frequency maybe about 2 Hz or less. Starting at such a low frequency allows thecapacity to be driven within the capability of the motor, and avoids thehigh inrush current that occurs at start up, or transients that occurwith the constant frequency and voltage power supply. The VCS is used toincrease the frequency and voltage to the motor using a pre-programmabletime profile stored within the system that accounts for torque and speedcharacteristics of the motor, which keeps the acceleration of thecapacity within the capability of the motor. As a result, the capacityis accelerated without drawing excessive current. This starting methodallows a motor to develop about 150% of its rated torque while drawingonly 50% of its rated current. As a result, the Vector Drive allows forreduced motor starting current from the AC power source, reducingoperational costs, placing less mechanical stress on the compressormotor, and increasing service life. The Vector drive also allows forprogrammable control of acceleration and deceleration of the capacity inits quest to track the load.

In order to effectively achieve energy efficiency gains the multi-motorcontrol also can translate be able to indicate an accurate refrigerantflow control. This is best achieved with active refrigerant expansiondevices that can actively alter the refrigerant flow. While conventionalmodulating expansion valves can achieve such goal to some extent,pulsing expansions valves can also be used, such as described in U.S.Pat. Nos. 6,843,064 and 5,675,982. Electronically controlled valves forrefrigerant control as described in U.S. Pat. No. 5,463,876 may also beused in embodiments of the invention.

FIG. 1 shows an exemplary vapor compression system 100. The systemincludes an HVAC system 110 that includes a Vector Control System 120configured to control operation of the HVAC system 110. The VCS 120connects to a condenser fan 145 that is located adjacent a condenser140. The condenser fan 145 is positioned to increase or decrease theamount of air flow over the condenser 140 as controlled by the VCS 120.A condensing fan motor is normally either single phase or three phaseand usually operates at 240 volts. The VCS system is designed to workwith all conventional condenser fans. In addition, the condenser fan 145may be capable of speed control such that the speed of the motor withinthe condenser fan 145 is configurable depending on the control signaloutputs from the VCS 120.

The HVAC system 110 also includes a compressor 135 that is alsocontrollable by the VCS 120. The compressor 135 may be any conventionalsingle phase or three phase compressor as typically used in an HVACsystem. In some embodiments, the compressor is a variable speedcompressor that uses frequency modulation to adjust power output of thecompressor motor. This control allows the compressor to speed up or slowdown according to the heating or cooling requirements placed on the HVACsystem 110. The ability to adjust speed and power requirements of thecompressor 135 can increase the overall system efficiency since thecompressor 135 can run at the proper capacity for a given load insteadof toggling on or off to maintain the desired temperature.

The HVAC system 110 also includes an evaporator 125 located adjacent ablower 130. The blower 130 is configured to move air across the coils inorder to deliver cold air to the target room or space. The motor withinthe blower 130 may be a single speed or variable speed motor.

Located between the condenser 140 and the evaporator 125 is an expansionvalve 150 that expands the coolant from the condenser back into a gas tobe directed to the evaporator 125 and complete the refrigeration cyclewithin the HVAC system 110.

A temperature and humidity sensor 155 is also located within the HVACsystem 155 that is configured to read the current temperature andhumidity and return that data to the VCS 120. As discussed above, theVCS can use the temperature and humidity to properly adjust the motoroperations of each motor within the system in order to maximize theefficiency of the system.

FIG. 2 shows more details on the VCS 120. As illustrated, the VCS 120includes a memory 220 configured to store data relating to the operationof the VCS 120. For example, the memory 220 may store state tables orlookup tables used by the VCS 120 to configure each of the motors withinthe system depending on a particular temperature or humidity.

TABLE 2 Example Lookup Table Condenser Evaporator Power FrequencyTemperature Temperature Cooling Draw (Hz) (° C.) (° C.) (W) (W) COP 6080 10 1953 1580 1.24 60 80 15 2389 1662 1.44 60 80 20 2906 1739 1.67 6080 25 3514 1812 1.94 60 80 30 4225 1885 2.24 50 40 −10 1375 623 2.21 5040 −5 1746 651 2.68 50 40 0 2192 673 3.26 50 40 5 2273 695 3.27 50 40 103348 720 4.65 50 40 15 4078 752 5.42 50 40 20 4922 795 6.19

The memory 220 is electrically connected to an efficiency determinationmodule 225 that is configured to read the data stored in the memory 220and determine how to adjust motors with the vapor compression system.The efficiency determination module 225 may include information on thetype of motors within the vapor compression system and how they can beadjusted to meet a particular target efficiency level. A sensor trackingmodule 230 that is connected to an I/O port 235 may be part of the VCS120, which is all running under the control of a processor 240. Theprocessor 240 may be configured by the efficiency determination module225 to determine the proper settings for each motor within a vaporcompression system.

FIG. 3 is a line graph that illustrates two dimensional control of speedand torque using a Vector Control System when applied in practice to acompressor. The X-Axis is a pressure ratio defined as ratio of high sidepressure to low side pressure of the compressor in a vapor compressionsystem. The Y-axis is a Coefficient of Performance (COP) ratio ofheating or cooling capacity to work required. As shown, with vectorcontrol technology in place the maximum compressor efficiency can onlybe achieved when motor speed and torque are controlled and varied at thesame time. In the example shown the compressor speed measured at 60 Hz,50 Hz and 40 Hz and data points were taken at 8 different pressureratios for each frequency. The goal to achieve the highest efficiencywas accomplished by applying the correct voltage/torque to the motor atlower pressure loads. This resulted in the optimal COP versus pressureratio.

Most conventional compressors are still powered using electrical motorsdesigned to run at a single speed since the motors are designed tooperate efficiently at their rated speed. Reducing compressor speed willnot necessarily result in higher efficiency without properly andintelligently implemented use of the vector drive technology. If thecontrols are not intelligent then lowering speeds can result in loweringmotor efficiency and potential damage to the motor windings. Electricalmotors are built with the right amount of slip to allow for maximumefficiency. They are designed to operate at their rated slip, whileoperating at maximum (design) load. The amount of slip, however, doesvary as the speed changes. As the slip strays from its ideal lag behindthe magnetic flux, the motor performance also drops. It is howeverpossible to return to optimal performance by supplying the proper amountof voltage to maintain the right amount of slip. Thus, adjusting thevoltage increases energy efficiency to optimize motor operation when themotor is running at a partial load. While the capacity can be adjustedto meet the thermal load by properly selecting the operating frequencyof the compressor motor, the energy efficiency optimization of providingtorque against the load can be best addressed with multi-motor controlof compressor and fan motors, the most energy efficient compressor motoroperation at any given torque and capacity is achieved by selecting avoltage that results in the optimum slip.

Slip to voltage relations of compressor/motor systems are usually notpublished or available from the manufacturer. However, the relations canbe experimentally determined so that the optimum slip is found bymeasuring the energy efficiency at any given pressure ratio and motorspeed (frequency) as a function of voltage.

In at least some of the previously described embodiments, one or moreelements used in an embodiment can interchangeably be used in anotherembodiment unless such a replacement is not technically feasible. Itwill be appreciated by those skilled in the art that various otheromissions, additions and modifications may be made to the methods andstructures described above without departing from the scope of theclaimed subject matter. All such modifications and changes are intendedto fall within the scope of the subject matter, as defined by theappended claims.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible sub-rangesand combinations of sub-ranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into sub-ranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 articles refers to groupshaving 1, 2, or 3 articles. Similarly, a group having 1-5 articlesrefers to groups having 1, 2, 3, 4, or 5 articles, and so forth.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A vapor compression system, comprising: acompressor having an inlet pressure and an outlet pressure; anevaporator and a first motor associated with the evaporator andconfigured to influence the temperature of the evaporator; a condenserand a second motor associated with the condenser and configured toinfluence the temperature of the condenser, wherein an increased speedof the motor reduces the outlet pressure and a decreased speed of themotor increases the outlet pressure; a refrigerant expansion device; anda vector control system configured to increase the energy efficiency ofthe vapor compression system given a particular thermal load bycontrolling the compressor torque by increasing the speed of the secondmotor to reduce the outlet pressure if the amount of energy required toincrease the second motor is less than the energy saved by reducing thecompressor torque.
 2. The vapor compression system of claim 1, whereinthe first motor comprises a first fan motor and wherein the first fanmotor controls airflow over the evaporator to influence the temperatureof the evaporator.
 3. The vapor compression system of claim 2, furthercomprising adjusting the speed of the first fan motor to alter theairflow across the evaporator and change the inlet pressure of thecompressor to increase the energy efficiency of the vapor compressionsystem.
 4. The vapor compression system of claim 1, wherein the secondmotor comprises a second fan motor, wherein the second fan motorcontrols airflow over the condenser to influence the temperature of thecondenser.
 5. The vapor compression system of claim 3, whereinincreasing the speed of the second fan motor increases the airflow overthe condenser to thereby reduce the outlet pressure.
 6. The vaporcompression system of claim 3, wherein decreasing the speed of thesecond fan motor decreases the airflow over the condenser to therebyincrease the outlet pressure.
 7. The vapor compression system of claim1, where the vapor compression system comprises an HVAC system thatprovides cooling to an airflow or liquid.
 8. The vapor compressionsystem of claim 1, wherein the vapor compression system comprises arefrigeration system providing refrigeration to an airflow or heattransfer fluid or suction to a low pressure receiver.
 9. The vaporcompression system of claim 1, wherein the vapor compression systemcomprises a heat pump that provides heating to an airflow or liquid. 10.The vapor compression system of claim 1, wherein the vapor compressionsystem comprises one or more reversing valves to allow the system tooperate as a heat pump.
 11. The vapor compression system of claim 1,wherein the refrigerant expansion device is a pulsing expansion valve.12. The vapor compression system of claim 1, wherein the vector controlsystem comprises a memory storing performance characteristics of thecompressor and the first and second motors.
 13. The vapor compressionsystem of claim 1, wherein the vector control system is configured toadjust a voltage to the compressor to optimize any compressor motor slipin order to increase the energy efficiency of the vapor compressionsystem.
 14. The vapor compression system of claim 1, wherein the vaporcompression system is configured to vary the amount of torque on thecompressor motor as part of satisfying the particular thermal load. 15.The vapor compression system of claim 1, wherein the vector controlsystem comprises a lookup table of frequency, cooling watts and powerdraw of the compressor at different condenser and evaporatortemperatures.